"I found a universal rule which appears to govern human actions or words more than any other: namely, to steer away from affectation at all costs, as if it were a rough and dangerous reef, and (to use perhaps a novel word for it) to practice in all things a certain sprezzatura which suppresses all artifice and makes whatever one says or does seem uncontrived and effortless."

Purposeful imperfection in dress - the elusive theory and practice of strategic dishevelment - is a phrase I coined in the pages of Town & Country magazine more than 20 years ago. However, I didn't invent the concept; I merely did the spadework to uncover its foundations. Like so many modern phenomena, the roots of this modus operandi can be found in the Italian Renaissance. The supreme author of that fecund period of etiquette writing was Mr Baldassare Castiglione, who set down the principles of perfected casualness in his study of court propriety, The Book of the Courtier, which was published in Venice in 1528.

His advice on the purposefully broken rule - which might these days involve leaving the buckles on your monk-strap shoes undone - was taken up by the courtiers of Urbino and Mantua, for whom he provided his instruction, and from there the concept spread north and east to Germany with the 16th-century Allemagne style of slashed breeches and doublet. Next it came to England, where it was seen in the nonchalant dress of the Cavaliers, which was so brilliantly described in the works of the poet Mr Robert Herrick. The nonchalance that conceals artistry also inspired the Regency bucks in the circle around Mr Beau Brummell and King George IV in the early years of the 19th century. And as a side note, we have only to look at the era of President Andrew Jackson and then the post-WWII Rebel Without a Cause period to see the same principle at work in the US.